1. Field of the Invention
The present invention relates generally to photosensing devices and is directed more particularly to such a photosensing device that is used to photosense an object with high reflectivity.
2. Description of the Prior Art
The role of camerae is vast such as a still camera purposed for prints, a camera for movie-picturing, or a CATV system which transmits an image to a far distance place, and an image senser that is used on a visual inspection apparatus which uses a television camera and an electronic processor to replace the human eye.
It can be further said that upon the picturing or photosensing an object with such camerae, an illumination device is essential where it is further noted that the lighting (illumination) techniques cannot be overlooked when the illumination device is used to irradiate on an object to be photo-sensed. For example, excelecnt photosensing cannot be obtained unless the lighting has been planned or revised to accomodate the different shaped object bodies such as light transparent objects of glass or the like, or powders, liquids and then objects with high light reflectivity such as metals, or flat plane objects and those with surface uneveness, lumpy solid objects, etc., because objects with such varied shape and optical characteristics will have to be photosensed by the camerae in a manner that the object features are cleverly picked up.
As an example, it is extremely difficult to photosense an object made of metal with a glossy surface (high light reflectivity). This is owing to the metal surface of the object having a high reflectivity for light where the light from a light source is reflected and the reflected light itself performs as a very strong high light so that the light source itself will be overlapped on the object upon being photosensed.
Therefore, upon photosensing such objects having high reflectivity for light, the normal direct lighting, which is to directly irradiate the light onto the object must be avoided, and it is known to be a commonsensed lighting method to apply an indirect illumination on the object with the diffused light through light diffusers or the like.
FIG. 1 and FIG. 2 respectively show examples of photosensing arrangements that use the prior art lighting methods.
On FIG. 1, reference numeral 1 designates an object to be photosensed or picked up, 2 an camera which photosenses or picks up the object 1 from above, and 3.sub.1, 3.sub.2 and 3.sub.3 light sources respectively for the irradiation (lighting) onto the object 1 which is placed under the camera 1. Reference numeral 4 denotes a light diffuser reflection board that is made of an opaque meterial and placed near the camera 2 between the object 1 and camera 2. A see through-hole 5 is formed through the light diffuser reflection plate 4 at a location that faces the camera 2 because the camera 2 must photosense the object 1 that is situated undrer the opaque light diffuser reflection board 4 through the through-hole 5. A support plate 6 is provided for supporting the object 1 that is located under the light diffuser reflection board 4 while at the same time it serves as the background to the object 1. As the support plate 6, such a plate which reflects the incident light by a small amount is used when the object 1 is to be photosensed whitish or bright, or to the contrary such a plate which reflects the incident light much is used when the object 1 is to be expressed blackish or darkish. At this time, it is needless to say that either of the light sources 3.sub.1 to 3.sub.3 do not irradiate directly upon the object 1 and as shown on FIG. 1, the lights from the light sources 3.sub.1 to 3.sub.3 are once reflected by the undersurface of the light diffuser reflection board 4 where such reflected lights irradiates upon the object 1 (indirect lighting) which is placed on the support plate 6 that is located under the light diffuser reflection board 4 as previously stated (see light paths A1, A2 and A3 in FIG. 1).
Now then, in the case of FIG. 1 as shown on the drawing, in order to photosense the object 1 by the camera 2, the see through-hole 5 formed through the light diffuser reflection board 4 is of the minimum diameter range that will enable the photosensing.
FIG. 2 shows another example of the prior art similar to that shown in FIG. 1, but the difference between the example of FIG. 2 and the example of FIG. 1 is that on the case of FIG. 1, the lights from light sources 3.sub.1 .about.3.sub.3 are once reflected by the light diffuser reflection board 4, which reflected lights are used to irradiate on the object 1, whereas on the example of the FIG. 2, the object 1 is surrounded by a cylindrical-shaped light diffuser cylinder 7 to which the lights from the light sources 3.sub.1 .about.3.sub.3, that are located outside the cylinder 7 are irradiated once on the light diffuser cylinder 7 which will pass the lights therethrough and diffuse the same. The light thus diffused is used to irradiate onto the object 1 that is located inside the light diffuser cylinder 7. In this case also, since the camera 2 will photosense the object 1 through the light diffuser reflection board 4, it is needless to say that a small diameter see through-hole 5 as same as the case in FIG. 1 is made available at a predetermined location on the light diffuser reflection board 4.
The same symbols indicate the same components on FIG. 2 respectively FIG. 1.
As shown on the examples on FIG. 1 and FIG. 2, although an indirect lighting method is applied to the object 1 to be photosensed which is a metal product or the like that has a mirror like surface with a high reflectivity, and through the see through-hole 5 provided at a portion of the light diffuser reflection board 4, the object 1 to be photosensed can be photosensed by camera 2, one problem arises. That is, when the object 1 is a body that tends to easily reflect light, the image of the through-hole 5 is made by the object 1, so that the camera 2 shall photosense the image of the see through-hole 5 overlapped on a part of the image of the object 1. Therefore, normally, in order to avoid this phenomenon, there is caused such a defect that the see through-hole 5 be made so small so far as it would not interfere the picturing of the object 1 or the object 1 is photosensed from the distance apart.
Concerning the above-mentioned defect, as the distance between the camera 2 and object 1 become long, the light sources 3.sub.1 .about.3.sub.3 which emit intensive lights become necessary which makes the device high costing and bulky in size.
Further, since the see through-hole 5 shall be made small in diameter, the amount of light incident to the camera 2 therethrough is reduced so that a high costing high sensitivity camera becomes required.